Steam Loco Boiler Pressure

gb1290

New member
Frankly, this is a minor nuisance, but if any of you know how to fix it (or tell me what I'm doing wrong), that would be great!

Anytime I idle a locomotive, boiler pressure will drop drastically. I will run the locomotive, park it somewhere, turn on the blower (usually 2 clicks, though I've experimented with the full range), go do something else, come back to it, and find that my locomotive whose safety valve had been going off every 10 seconds while running had suddenly lost 50psi+ over the course of maybe 10 minutes. I haven't read up on the law of thermodynamics in a while (I studied history), but that just doesn't seem right.

Speaking of the safety valve, building up steam pressure while running seems to be way too easy. So long as there is some water or coal (doesn't seem to matter the amount) in the boiler/firebox, and the train is running, there will be max pressure and the safety valve will go off more than it doesn't. This seems to be true regardless of whether I change the engine spec.

Note: I typically use one of Ben Neal's locos (updated to TS12 by philskene), though I've tested this with others (payware and freeware) and get similar results.

So, am I a guru of building steam while on the run or is that just how the game works? And how do I keep steam pressure at a reasonable rate while idling?

Thanks!
 
Really depends on the engine spec, AND which game it's in. 09, 10, 12, mac, mac2, TANE all seem to respond a little different to the same spec. The first few years of engines I made, I didn't put any real concern to the specs (not knowing all much about what I was doing at the time) and as a result, boiler PSIs are everywhere, brake pressure is all out of whack, max speeds and accelerations are all wrong. I will be adding to my K&L updates page an entire library of new engine specs for all the engines i've made so far. So there may end up being one in there you can use with your engines that aren't behaving correctly.

There is an asset on the DLS which contains an excel spread sheet where you fill in certain fields relating to the real engines performance and it'll fill out fields that you need to add to the engine spec to make it accurate. I've been using that since last October and everything i've made since has a much better performance record in CAB/Realistic mode now. I don't remember what the asset kuid is but I can try to find it.

Keep your eyes out for the new specs coming in the following week or two on the K&L site.
 
If you have the blower on, the coal will burn faster, the water will get hotter, hence the safety's going off.
The more the safety's go off, the less water you have & because the coal is burning quickly & you ain't shovelling
more on, your fire will be dying & giving less heat, the pressure will drop.
 
@ Steve, if this is the spreadsheet by Bill Frock, aka Billegulla, then try this: "Universal steam e-specs 09" <KUID2:81997:51009:3> I believe it will generate especs that will run but not optimum by any means.

Bill and I've agreed on many of the problems we see with the steam physics implementation in Trainz (in Bill's case, that he saw as he passed on a few years back). The worst problem we both agreed on is that the game gets significantly more work out of the cylinders in its simulation than is physically possible based on the dimensions you specify and steam pressure admitted. To the typical user and espec developer this is mostly masked by the wheelslip now activated with steam in Trainz. Due to the excessive force produced at the rails this requires a very reduced throttle/reverse when starting even if you disable the wheelslip settings to the point where adhesive wt to TE rations of 4 would not produce slip at starting with full throlttle/reverser settings.

Bill's solution to the excessive TE was to specify reduced cylinder volumes that varied often significantly from actual dimensions. He used a varying ratio based on a function of drive wheel dia. I came up with similar results but I didn't find a relationship between the excess of power produced and wheel dia. I found that cylinders with only 50-60% the size of the real loco's will output about the correct force in most all cases. Bill's spreadsheet was based on some ingame testing and some intuition. Many of his inputs are rather arbitrary. My spreadsheets are based mostly on mechanics, thermodynamics and a lot testing in the game. In effect I design a steam loco that is say 60% the size of the real one with respect to boiler and cylinder size and it produces 100% of the rated power of the real one in the game's simulation.

I've pulled my dynacar behind many steam locos recording data from the runs at 1 sec intervals. I record engine data, bogie data, steam epsec data, and train data at the start of each run and during the run I record 30 params each time interval. Post processing the data shows the same trend - the power output far exceeds that which the "real world" cylinders can actually produce.

Bob Pearson
 
@gp1290
Anytime I idle a locomotive, boiler pressure will drop drastically. I will run the locomotive, park it somewhere, turn on the blower (usually 2 clicks, though I've experimented with the full range), go do something else, come back to it, and find that my locomotive whose safety valve had been going off every 10 seconds while running had suddenly lost 50psi+ over the course of maybe 10 minutes.
The steam espec is fairly complicated and in many cases not really intuitive. At idle 2 parameters will effect the boiler temperature pretty directly: min-fire-temp and boiler-heat-loss. In particluar if the heat loss tag is too high the boiler will cool off fast and loose pressure due to condensation of steam back to water. If the blower is on at idle and it still doesn't steam it's possible the steam-blower-effect multiplier tag value is too low and/or the blower-flow tag is too large. An outside possibility is the idle-efficiency is hosed up. burn-rate-idle is another possibility but while I haven't tested any of this I suspect is not used when the blower is on - though I could be wrong.

BTW the blower goes to 50% of the blower-effect value at 1st click and then +10% each additional up to 100%. The blower-effect tag is the fraction of the draft effect (the game calculates internally) based on the design point setting specified in the espec.

I'd look 1st at heat-loss but all mentioned could conceivably compound the problem.

Speaking of the safety valve, building up steam pressure while running seems to be way too easy. So long as there is some water or coal (doesn't seem to matter the amount) in the boiler/firebox, and the train is running, there will be max pressure and the safety valve will go off more than it doesn't. This seems to be true regardless of whether I change the engine spec.
Boilers popping safeties is imo a function of improperly designed especs (compounded by N3V's steam physics simulation problems) and I've mentioned one probably cause in the post above where steam flow rates are severely restricted to get a more realistic power output.

Another is that the safety valve flow rates must be designed by regulation to limit overpressure to 9 psig or so (IIRC) in the US. Imo most safety flow rates in especs probably can't meet this "legal" requirement. I bypass any assumption as to what else is going on and assume the max evap capacity of the boiler must be considered. I use 1/3 of it for the low and 2/3 of it for the high. Probably overkill but while I pop safeties with some frequency they usually shut down after a minuite or so. A cautionary note here: Regardless of what you might read in the docs: steam flow to the steam chest is specified in mols/second (the molar mass of water is 0.018kg/mol) and steam flow from safeties and steam blower is specified in kg/sec.

Of course max-fire-temperature, firebox-heating-surface-area, firebox-thermal-conductivity, firebox-efficiency, and the boiler efficiencies along with ideal-coal-mass, burn rates and design point specified all effect evaporation rates. Adjusting just 1 tag value and getting a realistic espec is a crap shoot. Getting an optimal one to simulate a specific real loco is asking a lot of any designer.

Bob Pearson
 
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